In a wider sense iatrogenic carcinogenesis means the induction of cancer by medical treatment. Some drugs have been now identified to be carcinogenic not only in experimental animals but also in man. For example, chlornaphazine used in the treatment of polycythemia has been proved to induce bladder cancer in 30% of the patients treated. This is also true for alkylating agents which are used as cytostatics in cancer treatment. Adjuvant chemotherapy must be used with due caution. There is probably one iatrogenic carcinoma in 10,000 cases. Hence, it is important to analyze the risk-benefit ratio of such drugs.